iq. s ] AASE— MEGASPOROPEYLLS OF CONIFERS 3°7 



(figs. 183, 186). At the base of the ovule each bundle passes into 

 a mass of short irregular tracheids of large caliber. From each 

 mass arises a small strand consisting of poorly developed xylem 

 soon replaced by elongated thickened cells without xylem markings. 

 Each strand passes upward in the thickened ridge of the ovule. 



Discussion 



Assuming that the megasporophyll in all the forms is a com- 

 posite organ, consisting of bract and axillary scale, the investigated 

 forms may be divided into four general groups based on the relation 

 of bract and scale to one another. 



In the first group the bract and scale are separate almost to the 

 base of the appendage and both are about equally prominent. 

 Here belong Ketelecria (fig. 36), Pseudotsuga, species of Abies, and 

 species of Larix. 



In the second group the bract and scale are separate as in the 

 first group, but the bract, at least in the later stages, is much 

 less prominent than the scale, and in certain instances appears 

 distinctly to be on its way to obliteration. In this group belong 

 species of Ab ies (2), species of Larix, Tsuga, Picea, Piuus (figs. 1, 2), 

 and species of Podocarpus and Dacrydium (4); Cedrus Libaui (2) 

 and the lower sporophylls of Pinus Banksiana (fig. 2) show the 

 bract in process of extinction. In species of Podocarpus the scale 

 has folded toward its dorsal side, thus forming the second integu- 

 ment or epimatium of the inverted ovule (fig. 182). 



In the third group the bract and scale are considerably to com- 

 pletely welded, but the fused structure shows some evidence of 

 its double nature. Within this group are Sciadopitys (2), Sequoia 

 (2), Cunninghamia (fig. 139), species of Arthrotaxis (1), Cryp- 

 tomeria (fig. 114), Taxodium, Thuja (tig. 85), Cuprcssus (fig. 59), 

 Chamaecyparis (fig. 102), Juni penis (fig. 113), Araucaria (fig. 153), 

 and Podocarpus dacrydioides (4). In young strobili of Araucaria 

 Rulci (fig. 161) and Cryptomeria japonica (fig. 126) the bract and 

 scale are distinct almost to the base, and the fused portion becomes 

 comparatively large in the subsequent development of the organ. 

 In Cuprcssus Benthamii (fig. 58), Thuja occidentalis, Chamaecyparis 

 Lawsoniana (fig. 103), and Juniperus communis the scale in the 



